Defrosting arrangements for refrigeration systems



Nov. 22, 1955 J. SWINBURNE 2,724,245

DEFROSTING ARRANGEMENTS FOR REFRIGERATION SYSTEMS Filed Sept. 30, 1952United States Patent Ofiiice 2,724,245 Patented Nov. 22, 1955 12,724,245 DEFROSTIN G ARRANGEMENTS FOR REFRIGERATION SYSTEMS JamesSwinburne, Syracuse, N. Y., assignor to Carrier Corporation, Syracuse,N. Y., a corporation of Delaware Application September 30, 1952, SerialNo. 312,377

Claims. (Cl. 62-415) This invention relates to defrosting arrangementsfor refrigeration systems and, more particularly, to a refrigerationsystem for use in transportation such as trailers or trucks for Coolingthe storage compartment thereof which is provided with defrosting meansfor removing frost from the evaporator when it collects thereon.

The chief object of the present invention is to provide a simple andeconomical defrosting arrangement for the evaporator of a refrigerationsystem.

An object of the present invention is to provide a refrigeration systemin which, during the defrosting cycle, evaporator pressure is increasedto a point corresponding to a temperature at least slightly above 32 F.to provide heat for melting frost fromthe exterior surfaces of theevaporator. i i

A further object is to provide a defrosting arrangement for arefrigeration system in which. the cooling arrangement of the primemover employed to drive the compressor of the system is utilized toreevaporate refrigerant condensed in the evaporator of the system duringthe defrosting cycle. Other objects of the invention will be readilyperceived from the following description.

This invention relates to a refrigeration system which comprises, incombination, a compressor, a condenser, a discharge line connecting thecompressor and the condenser, an evaporator, a liquid line connectingthe evaporator and the condenser, expansion means in the liquid line, asuction line connecting the evaporator and the compressor, means in saidsuction line for maintaining evaporator pressure at 'a desired pointduring a defrosting cycle, a second evaporator, a capillary lineconnecting the second evaporator with the suction line at a pointbetween said means and the evaporator, a fifth line connecting thesecond evaporator with the suction line at a point between said meansand the compressor, means for evaporating refrigerant in said secondevaporator, a sixth line connecting the discharge line and the liquidline at a point between the expansion means and the evaporator and meansfor closing said sixth line.

The attached drawing illustrates a preferred embodiment of theinvention.

Referring to the drawing, there is shown a refrigeration system whichincludes a compressor 2 connected by discharge line 3 to condenser 4.Preferably compressor 2 is driven by an internal combustion: engine 5having its own cooling system. Engine 5 may be air cooled as by fan 6which serves to pass air over the surfaces of the engine. If desired, ofcourse, a water cooling system may be used. Condenser 4 is connected toa receiver 7 by line 8. Receiver 7 is connected to evaporator 9 by.liquid line 10. Expansion means 11 such as an expansion valve is placedin liquid line 10 and regulates flow of refrigerant to evaporator 9.Expansion valve 11 is regulated by means of a bulb 12 placed in contactwith the suction line 13 of the refrigeration system. A solenoid valve14 may be placed in liquid line 10 at a point between expansion valve 11and receiver 7 for a purpose hereinafter explained. Preferably, a smallreceiver 15 is placed in liquid line 10 at a point between expansionvalve 11 and solenoid valve 14.

Evaporator 9 is placed in the storage compartment 16 of a trailer 17.Evaporator 9 is contained in a casing 18 provided with dampers 19. A fan2*!) serves to pass air from compartment 16 through evaporator 9 in heatexchange relation with refrigerant therein, thus cooling the storagecompartment. The evaporator 9 may be provided with the usual drip pan 21as hereinafter explained.

Suction line 13 connects evaporator 9 with compressor 2. A holdbackvalve 22 is placed in suction line 13 to regulate evaporator pressure.It will be appreciated valve 22 offers little restriction to the flow ofgaseous refrigerant through line 13 under normal conditions of operationbecause normal suction pressure will be below its design setting; thus,there will be only a minor pressure drop across valve 22. p

A small reevaporator 23 is provided which is connected to suction line13 at a point between evaporator 9 and holdback valve 22 by a capillarytube 24. The exit end of reevaporator 23 is connected to suction line 13at a point between holdback valve 22 and compressor 2 by a line 25.Reevaporator 23 is so placed in the system that refrigerant therein isplaced in heat exchange relation with heated air provided by the enginecooling fan 6. If a water cooling system is employed to cool engine 5'it will be appreciated the heated water may be placed in heat exchangerelation with refrigerant in reevaporator 23.

A fan 26 is employed to pass air in heat exchange relation withrefrigerant in condenser 4 to condense the refrigerant. Fan 26 and fan20 may be mounted on the same shaft 27 and may be connected to engine 5to be driven thereby. A magnetic clutch 28 may be employed, if desired,to permit operation of fans 20, 26 to be discontinued while continuingoperation of the engine S.

A hot gas line 30 connects discharge line 3 with liquid line 14 at apoint between the entrance end of the evaporator and the expansion valve11. A second solenoid valve Si is placed in line 30 to close the same.Solenoid valves 14 and 31 may be actuated by any suitable means.Preferably, these valves are actuated by a thermostat (not shown)responsive to the temperature of storage compartment 16, although, ifdesired, they may be actuated by a manually movable switch (not shown).

Considering the operation of the refrigeration system during its normalcooling cycle, compressor 2 compresses gaseous refrigerant andsuppliesthe hot gaseous refrigerant to condenser Fan 26 passes air in heatexchange relation with gaseous refrigerant in condenser 4 to condensethe same, the condensed refrigerant passing to receiver 7. From receiver7, the condensed refrigerant passes through liquid line 10 to evaporator9, expansion valve 11 metering the amount of refrigerant supplied to theevaporator. Fan 2% draws air from storage compartment 15 within casing18 and passes the air in heat exchange relation with refrigerant inevaporator 9 thereby cooling the air and, evaporating the refrigerant.The evaporated refrigerant returns to compressor 2 through line 13.. itwill be appreciated holdback valve 22, as stated above, offers littleresistance to passage of gaseous refrigerant through line 13 duringnormal operation of the system.

Frost collects on the exterior surfaces of evaporator 9 during thenormal cooling cycle thus reducing the efliciency of the refrigerationsystem. It is necessary, therefore, to remove the frost from theexterior surfaces of the evaporator in order to maintain normal coolingoperation. When sufficient frost has collected on the evaporator, anysuitable means may be employed to place the refrigeration system in itsdefrosting cycle.

Considering operation of the refrigeration system during the defrostingcycle, solenoid valve 31 is opened and solenoid valve 14 is closed.Closing of valve 14 prevents passage of liquid refrigerant from receiver7 to evaporator 9. Opening of valve 31 permits hot gaseous refrigeranttopass to the evaporator through line 30.

Preferably, operation of fans 20 and 26 is discontinued. If desired, thedampers 19 in casing 18 may be closed to prevent hot air passing intostorage compartment 16.

Since the holdback valve 22 is set to a predetermined point, evaporatorpressure is increased to a point corresponding to at least 32 F. thusproviding heat for thawing the frost collected on the exterior surfacesof the evaporator.

The hot gaseous refrigerant supplied to evaporator 9 under suchpredetermined pressure is placed in heat exchange relation with thefrost collected on the exterior surfaces of the evaporator thawing thefrost and condensing the refrigerant. The liquid refrigerant flowsthrough suction line 13 until it arrives at holdback valve 22. Valve 22may be set to prevent suction pressure from rising above to p. s. i. g.The pressure built up ahead of valve 22 forces the liquid refrigerantthrough capillary tube 24 into reevaporator 23. The hot air stream fromengine 5 passes in heat exchange relation with refrigerant inreevaporator 23 thereby evaporating the refrigerant. Gaseous refrigerantreturns to the cornpressor through line 25 and that portion of suctionline .13 between holdback valve 22 and compressor 2. Capillary tube 24and reevaporator 23 provide sufiicient pressure drop and sufiicientevaporator surface so thatthe liquid refrigerant condensed in evaporator9 is re-evaporated thus preventing liquid pumping by the compressor.

.When the frosthas been removed from the exterior surfaces of evaporator9 the defrosting cycle is discontinued and normal cooling operation ofthe refrigeration system is resumed.

Receiver 15 contains a minor quantity of liquid refrigerant. Whensolenoid valve 14 is closed at the beginning of the defrosting cycle,liquid in receiver 15 flows through expansion valve 11 intotheevaporator 9 thus providing sufiicient refrigerant to begin thedefrosting cycle. In addition, such receiver 15 assures that sufficientrefrigerant is present in the system during the defrosting cycle toinsure removal of frost from the evaporator.

. If desired, solenoid valve 14 may be omitted, expansionvalve 11closing liquid line 10 during the defrosting operation. However, it isgenerally desirable to employ valve 14 as a safety measure to assurethat line 10 is closed to passage of refrigerant from condenser 4 toevapto equalize the high and low side of the compressor at suctionpressure. I

It will be understood the defrosting arrangement of the presentinvention may be employed to heat storage compartment 16 as well as toremove frost from the evaporator 9 when it is desired. For example, toprevent the temperature of the compartment falling below 32 F.

While the present invention has been described in connection with arefrigeration system employed in transportation, it will be understoodthe defrosting arrangement may be employed, if desired, in stationaryapplications.

The present invention provides a simple and inexpensive defrostingarrangement for the evaporator of a re frigeration system. It is adaptedfor use with refrigeration systems employed in transportation. Thearrangement may be actuated automatically or manually as desired. Thedefrosting arrangement assures that only gaseous refrigerant returns tothe compressor during the 4 defrosting cycle thereby eliminating wear onthe valves of the compressor and reducing greatly the noise ofcompression. The provision of a small receiver or reservoir in theliquid line assures sufiicient refrigerant present in the low side ofthe system during defrosting.

While I have described a preferred embodiment of the invention, it willbe understood the invention is not limited thereto since it may beotherwise embodied within the scope of the following claims.

I claim:

1. In a refrigeration system, the combination of a compressor, acondenser, a discharge line connecting the compressor and the condenser,an evaporator, a liquid line connecting the evaporator and thecondenser, expansron means in said liquid line, a suction lineconnecting the evaporator and the compressor, a holdback valve in saidsuction line for maintaining evaporator pressure at a desired pointduring a defrosting cycle, a second evaporator, a capillary lineconnecting the second evaporator with the suction line at a pointbetween said holdback valve and the evaporator, a fifth line connectingthe second evaporator with the suction line at a point between saidholdback valve and the compressor, means for evaporating refrigerant insaid second evaporator, a sixth line connecting the discharge line andthe liquid line at a point between the expansion means and theevaporator, and a solenoid valve closing said sixth line during thenormal cooling cycle of the refrigeration system.

2. A refrigeration system according to claim 1 in which a secondsolenoid valve is provided in the liquid line at a point between theexpansion valve and the condenser to prevent passage of liquidrefrigerant from the condenser to the expansion means during thedefrosting cycle of the refrigeration system.

3. A refrigeration system according to claim 2 in which a reservoir isprovided in the liquid line between the expansion means and the secondsolenoid valve.

4. In a defrosting arrangement for a refrigeration system, thecombination of a holdback valve'in the suction line to increaseevaporator pressure to a point at least corresponding to an evaporatortemperature of 32 F., a reevaporator, a capillary line connecting thereevaporator to the suction line of the system at a point between thevalve and the evaporator, means for evaporating liquid refrigerantcollected in the suction line during the defrosting operation in there-evaporator, and a line to return gaseous refrigerant from saidre-evaporator to the compressor.

5. In a defrosting arrangement for a compressor-condenser-expanderrefrigeration system, the combination of a holdback valve in the suctionline to increase evaporator pressure to a point at least correspondingto an evaporator temperature of 32 F., a re-evaporator, a capillary lineconnecting the re-evaporator to the suction line of the system at apoint between the valve and the evaporator, a line connecting there-evaporator to the suction line at a point between the valve and thecompressor to return gaseous refrigerant from the reevaporator to thecompressor, means for passing a heating medium in heat exchange relationwith liquid refrigerant in the re-evaporator to evaporate the liquidrefrigerant, a line connecting the discharge line of the refrigerationsystem with the entrance end of the evaporator of the refrigerationsystem, and a solenoid valve placed in said line to close the sameduring the normal cooling cycle of the refrigeration system.

References Cited in the file of this patent UNITED STATES PATENTS2,455,421 Kirkpatrick Dec. 7, 1948 2,459,173 McCloy Jan. 18, 19492,526,379 Maserit z' Oct. 17, 1950 2,573,684 Binder Nov. 6, 1951

